A tire serves to withstand the load of automobiles, to reduce impact with a road surface, and to transfer a driving force or braking force of an automobile to the ground. In general, the tire refers to a complex of fiber/steel/rubber and normally has a structure as shown in FIG. 1.
Tread (1): a portion that is in contact with the road surface. It should afford frictional force required for driving and braking, have good wear resistance, withstand external impact, and have minimal heat generation.
Body ply (or carcass) (6): a cord layer inside the tire. It should support a load, withstand impact, and have strong fatigue resistance to bending and stretching while the vehicle is running.
Belt (5): located between the body plies. It consists of steel wire in most cases, reduces external impact, and maintains a large area of contact of the ground to the surface of the tread to afford excellent vehicle running stability.
Side wall (3): a rubber layer between a part below a shoulder (2) and a bead (9). It serves to protect the inner body ply (6).
Inner liner (7): located inside the tire instead of a tube. It prevents air leakage to enable a pneumatic tire.
Bead 9: square or hexagonal wire bundle formed of rubber-coated steel wire. It serves to stabilize and fix the tire in a rim.
Cap ply (4): a special cord located on a belt of a radial tire for some passenger cars. It minimizes movement of the belt during automobile running.
Apex (8): triangular rubber filler used to minimize dispersion of the bead, reduce external impact to protect the bead, and prevent air inflow during molding.
Recently, a tubeless tire in which high pressure air of about 30˜40 psi is injected without using a tube has become widely used. In order to prevent inside air from leaking outside during automobile running, an inner liner having a high gas barrier property is disposed in an inner layer of the carcass.
Previously, a tire inner liner consisting mainly of rubber components such as butyl rubber or halobutyl rubber having relatively low air permeability was used, but in order to achieve a sufficient gas barrier property of the inner liner, the content of the rubber components and the thickness of the inner liner should be increased.
However, if the content of the rubber components and the thickness of the tire are increased, there are problems in that the total weight of the tire is increased and the fuel efficiency of automobiles is lowered.
Moreover, since the rubber components have relatively low heat resistance, there were problems in that air pockets may be generated between rubber in the inner surface of a carcass layer and an inner liner, or the shape or physical properties of the inner liner may be changed in a vulcanization process of a tire or in an automobile running process during which repeated deformations occur under a high temperature condition.
In addition, in order to adhere the rubber components to a carcass layer of a tire, a vulcanizing agent should be used or a vulcanization process should be applied. For this, it was difficult to secure sufficient adhesion force.
Accordingly, various methods have been suggested to decrease the thickness and weight of the inner liner to increase fuel efficiency, reduce changes in the shape or physical properties of the liner during tire molding or automobile running, and the like.
However, previously known methods have limitations in maintaining excellent air permeability and tire moldability while sufficiently reducing the thickness and weight of the inner liner.
Moreover, the inner liner manufactured by the previously known methods exhibited reduction of its own physical properties, and had cracks generated in the film and the like in the tire preparation process during which repeated deformations occur at a high temperature or in an automobile running process during which repeated deformations occur and high heat is generated.